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Vernal Pond Field Trip

Mar 31, 2017 2:15 PM

By Mike Bottini

Last weekend’s Long Island Natural History conference at Brookhaven National Lab included a presentation on the creatures that utilize vernal ponds in at least some part of their life history, and the interesting adaptations they have evolved to cope with the ephemeral nature of that habitat.Vernal ponds, sometimes called vernal pools since some can be better described as a puddle than a pond, are freshwater wetlands that periodically become completely dry and therefore cannot support a population of fish. The lack of fish is a key element of vernal ponds that makes them ideally suited for mole salamanders, frogs and toads to congregate there, mate, lay eggs, go through their respective larval stages and metamorphose into their terrestrial adult forms without being subject to fish predation.

The wet-dry cycle of vernal ponds is driven by precipitation, evaporation and transpiration. The average annual 47 inches of precipitation here on Long Island is evenly distributed throughout the year, with each month averaging between three and four inches. However, the average net recharge to the water table and freshwater ponds during the growing season when trees and shrubs and other plants are leafed-out is zero, a result of water loss due to transpiration and evaporation. This usually initiates a gradual loss of standing water in our vernal ponds beginning in late May and accelerating through the summer months, and a gradual recharge of those same vernal ponds in the fall as leaves turn and fall.

As a follow-up to Saturday’s presentation, Matt Burne and Leo Kenney, co-authors of “A Field Guide to the Animals of Vernal Pools,” led a Sunday morning field trip to a vernal pond in the Brookhaven area. Since both reside in Massachusetts and are not familiar with the locations of the vernal ponds here on Long Island, a small group of Long Island naturalists met them on Saturday evening to introduce them to some Long Island brew, and reconnoiter some of our favorite vernal ponds.

Joe Jannsen and John Turner had checked a few sites earlier, and over dinner and pints at the BrickHouse Brewery in Patchogue we learned that water levels were extremely low. In fact, there was no standing water in most of the vernal ponds they had visited. Over the past year—March 2016 through February 2017—total precipitation recorded was 33 inches, down 14 inches from normal, or 30 percent. Many of our vernal ponds will not support a 2017 cohort of salamanders, frogs and toads, but the lack of annual recruitment is another aspect of their life history that they have adapted to.

We did manage to find a beautiful vernal pond set in a forest that, although its water level was significantly lower than usual, had plenty of standing water to support a variety of vernal pond creatures. Topping the list in terms of numbers were fairy shrimp and daphnia, both important sources of food for amphibian larvae. Two types of caddisfly larvae structures were found: the “log-cabin” made of stems and woody material and the “cigar-tube” made of rolled leaves. Both structures provide protection, camouflage and ballast for their inhabitants.

Springtails danced along the pond’s surface, using the tension of the water to stay high and dry. Spring peepers and wood frogs were calling, and one individual of the latter was found on the damp forest floor near the edge of the water, but the frog’s egg clusters could not be found. The most interesting find was a one-inch-long salamander larva, a strange, fragile looking creature with prominent feathery gills protruding from its neck.

Could this be a marbled salamander hatched from an egg laid last fall, or a tiger salamander from an egg laid this winter? Most agreed we had a tiger, as the marbled would have been noticeably larger at this time of the year. Tiger salamanders are known to exit their underground haunts and head to their vernal breeding ponds during warm, rainy spells as early as January. It’s one of the many amazing animals found in our vernal pond communities.